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Re: Alxasaurus and segnosaurs
On Tue, 6 Feb 1996, Jeffrey Martz wrote:
> > > Is is remotely possible the segnosaurs are paraphyletic?
> > I think that this would SUCK! Or as people say from Seattle LAME!
> > IMHO, I think you mean Polyphyletic?
> I mean some being theropods and others being sauropodomorphs, or some
> being sauropodomorphs and others being ornithischins or whatever, and
> there just being a lot of covergence.
That is, indeed, polyphyly. "Paraphyletic" refers to a (usually
unspecialized) basal assemblage whose (usually specialized) descendants are
classed outside the group, while "polyphyletic"
refers to unrelated groups being classed together.
For example, the "family Pongidae," supposed to include orang-utans,
chimpanzees, and gorillas, but not humans, is paraphyletic (these animals
are indeed descended from a common ancestor, but there is another animal,
the human being, that is also descended from this common ancestor but is
not included in the taxon).
The "Pachydermata," on the other hand, was a taxon conceived to hold
tapirs, horses, rhinos, elephants, and hippos. This assemblage is
polyphyletic, the features supposedly uniting this group having appeared
independently in each lineage.
> LN Jeff
Pacific Lutheran University
Tacoma, WA 98447
"If you can't convince them, confuse them." -- Harry S. Truman